1. Field of the Invention
The present invention relates in general to fuel injection systems for automotive internal combustion engines, and more particularly to the fuel injection systems of a type which can vary or control emission of the engine in accordance with an area where the vehicle is usually used.
2. Description of the Prior Art
Hitherto, in automotive internal combustion engines, various types of fuel injection systems have been proposed and put into practical use. One of them is of a type which comprises fuel injectors for injecting fuel into intake ports of combustion chambers, an engine speed sensor for detecting the engine speed, an air flow meter for detecting the amount of air led into the engine and a processing unit which calculates an amount of fuel injected by each of the fuel injectors by processing the detected engine speed and the detected amount of intake air.
In such fuel injection system, an instruction pulse signal corresponding to the calculated injection amount of fuel is practically applied to each fuel injector to cause the same to inject a metered fuel into the corresponding combustion chamber, so that the metered fuel is appropriately mixed with the intake air in the combustion chamber and ignited by an ignition plug to produce a high combustion pressure in the combustion chamber. With this, a desired torque is outputted from a crankshaft of the engine. In the processing unit, by processing the detected engine speed and the detected intake air amount, a basic amount of injected fuel is calculated. In practice, with reference to the calculated basic amount of injected fuel, the amount of fuel actually injected into each combustion chamber is so controlled that the air/fuel mixture of the engine shows a stoichiometric ratio (for example, .lambda.=14.7). Usually, with this control, the output and emission characteristics of the engine are improved.
Regarding emission standards of motor vehicles, the regulation value changes depending on the area where the vehicle is practically used, that is, for example, between an urban area and a rural area, between a midtown area and a suburban area, between Japan and USA, etc.,. Accordingly, hitherto, for each type of motor vehicles, the fuel injection system thereof has had a hardware and a software which are exclusively designed for clearing the emission regulation value of the area where the vehicle is usually used. Thus, when the vehicle is thereafter planed to be used in other area, it becomes necessary to change the hardware and the software of the fuel injection system of the engine, which is troublesome and requires modifying costs.
In fact, in case of motor vehicles used in California of USA where a very severe regulation of exhaust gas has been adopted, the fuel injection system for the vehicles has been designed to give priority to emission reduction over power of the vehicles. This means that the fuel injection system for the vehicles used in California needs a specialized designing and thus increases manufacturing costs.